NMR thermal analyzer

ABSTRACT

A method is provided for carrying out proton magnetic resonance thermal analysis measurements. To this end, the method provides locating a sample within a coil forming part of an RF tuned circuit and applying a magnetic field to the sample. The sample is heated in accordance with a predetermined temperature regime. Pulsed RF energy is applied to the coil to generate a pulsed RF electromagnetic field which is applied to the sample. The magnitude of the magnetic field is adjusted to insure that the NMR frequency of the sample is substantially identical to the RF frequency. The resonant frequency of the tuned circuit is adjusted to compensate for temperature induced changes in the tuned circuit components and the sample. The energy of the pulsed RF energy is adjusted to obtain an optimum output from the RF tuned circuit. The RF tuned circuit output is recorded as a function of either time or temperature of the sample. A proton magnetic resonance thermal analyzer is further provided as well as a high temperature heater probe for nuclear magnetic resonance measurements.

The present invention relates to nuclear magnetic nuclear resonance(NMR), and, in particular, to the thermal analysis of various substancesby use of the process known as proton magnetic resonance thermalanalysis (PMRTA).

BACKGROUND OF THE INVENTION

It is known to take such NMR measurements with the sample held at, ornear, room temperature by use of commercially available equipment knownas an NMR spectrometer. One such spectrometer which is commerciallyavailable is the BRUKER MINISPEC manufactured by Bruker of Germany.While this device has a price which is within an acceptable range, thedevice suffers from the disadvantage that the temperature range at whichmeasurements can be taken is limited. As the temperature controlledprobes used with this device are water cooled, the maximum temperatureat which any measurement can be taken is approximately 100° C.

Another NMR spectrometer which is commercially available is that soldunder the trade name MAGNEPULSE PC/AT 2000 by Auburn International Inc.of Danvers, Mass., U.S.A. Again this device operates at a substantiallyconstant temperature.

However, many substance-q such as coal, NYLON, KEVLAR (Registered TradeMarks) and generally any solid, semi-solid or liquid organic materialincluding polymers are desirably subjected to PMRTA. As such substancesare heated they undergo various transformations from an initialequilibrium state to a final equilibrium state. The intermediate statesare inherently non-equilibrium and transient. Thus, in order to captureinformation about these intermediate states, the measurement techniqueswould ideally be instantaneous. In practice this ideal is never met butpractical results can be achieved if the time resolution of the in-situmeasurement is adequate to monitor phenomena of interest. The NMRproperties, which reflect the physical and chemical properties of thesubstance, are required to be recorded and monitored as a function oftemperature and time as the substance is subjected to a controlledtemperature program.

The measurement difficulties arise because of the continually changingnature of the properties of the specimen and the measurement equipmentduring the course of the analysis. For example, the dielectricproperties of the specimen, coil resistance, and other electricalproperties of the resonant radio frequency (RF) circuit change duringthe temperature changes. An analogy may be drawn to attempting to takefast exposure photographic snap shots of an object having a variabledistance from the lens while the lens itself is changing its shape.

OBJECT OF THE INVENTION

It is the object of the present invention to provide a method of, andapparatus for, carrying out proton magnetic resonance thermal analysismeasurements. This method and apparatus is capable of beingsubstantially automated.

In carrying out such measurements, it is necessary to heat a smallsample of the material to be analyzed to high temperatures in theabsence of other hydrogen or proton containing material. The sample isheld within a probe which is itself located within a magnetic field. Theperformance of the probe is largely dependent upon its mechanical,electrical and structural properties. It is an ancillary object of thepresent invention to provide a probe construction which enables theprobe to be fabricated without undue difficulty and which enablesaccurate results to be achieved from the NMR measurements.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is disclosed amethod of carrying out proton magnetic resonance thermal analysismeasurements, said method comprising the steps of:

i) locating a sample within a coil forming part of an RF tuned circuitand applying a magnetic field to said sample,

ii) heating said sample in accordance with a predetermined temperatureregime,

iii) applying pulsed RF energy to said coil to generate a pulsed RFelectromagnetic field which is applied to said sample, and thereaftersubstantially simultaneously,

iv) adjusting the magnitude of said magnetic field to ensure that theNMR frequency of said sample is substantially identical to the RFfrequency,

v) adjusting the resonant frequency of the tuned circuit, if necessary,to compensate for temperature induced changes in the tuned circuitcomponents and sample,

vi) adjusting the energy of said pulsed RF energy to obtain an optimumoutput from said RF tuned circuit,

vii) recording the RF tuned circuit output as a function of either thetime or the temperature of said sample, and

viii) repeating steps (iv) to (vi) as necessary at each desired time orsample temperature to obtain an optimum RF tuned circuit output, andrepeating step (vii).

Preferably the power of the RF energy Is adjusted by adjusting the pulsewidth of the RF pulses.

In accordance with another aspect of the present invention, there isdisclosed a proton magnetic resonance thermal analyzer comprising an RFtuned circuit including an RF coil into which an NMR sample isinsertable, said RF coil being locatable in a magnetic field, magneticfield strength means to adjust the magnitude of said magnetic field, RFpulse means connected to said RF tuned circuit to supply same withpulsed RF energy, an RF controller connected to said RF pulse means toadjust the magnitude of said RF energy, an RF tuner connected to said RFtuned circuit and a heater to substantially increase the temperature ofsaid sample above ambient temperature, wherein each of said magneticfield strength means, said RF controller, said RF tuner and said heateris connected to a central processing unit and is both simultaneously andindividually controlled thereby.

According to a still further aspect of the present invention, there isdisclosed a high temperature heater probe for nuclear magnetic resonancemeasurements, said probe comprising an elongate body having an openingat one end, a tubular former carrying an RF coil located within saidopening with the electrical connections to said RF coil passing throughsaid body, the interior of said former being dimensioned to receive aNMR sample holder, a heater coil non-inductively wound along saidelongate body and a layer of heat resistant substantially protondeficient cement covering said heater coil and through which saidelectrical connections to said RF coil pass.

Preferably the opening in said body takes the form of a slottedcylindrical opening, the RF coil connections passing through the slot.In addition, the substantially proton deficient cement is preferablyalumina-silicate cement.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the present invention will now be described withreference to the drawings in which:

FIG. 1 is a schematic side elevation of a prior art manually operableproton magnetic resonance thermal analyzer,

FIG. 2 is a schematic side elevation and block diagram view of thepreferred embodiment of a substantially automatic proton magneticresonance thermal analyzer based upon the above mentioned BRUKERMINISPEC.

FIG. 3 is a perspective view of the probe of the preferred embodiment,

FIG. 4 is a centrally located longitudinal cross-sectional view throughthe probe of FIG. 3, and

FIG. 5 is an enlarged portion of FIG. 4.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

As seen in FIG. 1, a pair of permanent magnet magnetic pole pieces 2 areprovided having a yoke 3 of adjustable magnetic reluctance. This cantake the form of a screw threaded member (not illustrated) which isrotatable to adjust the reluctance. Alternative arrangements includecurrent adjustment for an auxiliary field coil. The electricaladjustment to be described in FIG. 2 is preferred over theabovementioned mechanical adjustment.

Between the pole pieces 2 is located an RF coil 4 which is connected inparallel with an adjustable capacitor C1 to form an RF parallel tunedcircuit. Series tuned circuit configurations are also possible. Acoupling capacitor C2 is also provided to connect the tuned circuit toRF input/output terminals T.

Within the RF coil 4 is a sample holder 5. A thermocouple 8 is locatedbelow the sample holder 5. Exterior to the RF coil 4 is a heating coil 6the operation of which is controlled via temperature controller 7 towhich both the heating coil 6 and thermocouple 8 are connected.

In operation, the temperature controller 7 is set to a predeterminedcontrolled temperature regime and the sample within the sample holder 5is heated in accordance with that regime. Pulsed RF energy is applied tothe RF tuned circuit via terminals T. The frequency of this energy issubstantially identical to the NMR frequency of the sample so that aninduced NMR signal is generated which forms the output of the apparatusand appears at terminals T at the cessation of the input pulse(s). TheNMR properties of the sample are thus measured both as a function oftime and temperature as the heating of the sample proceeds.

From time to time it is necessary to adjust the strength of the magneticfield extending between the pole pieces 2 in order to make the NMRfrequency (which is magnetic field strength dependent) equal to the RFinput frequency. In addition, it is desirable to adjust the power of theRF input in any conventional way, such as by pulse width control, inorder to achieve an optimum output at the terminals T.

It is also necessary to tune the resonant RF circuit which includes thesample. This normally involves the adjustment of a variable capacitor tochange the resonant frequency of the circuit to track the temperatureinduced changes in both the sample and the tuned circuit. In thisconnection it needs to be borne in mind that the sample forms part ofthe tuned circuit. An impedance matching capacitor may also be adjustedif desired.

Once these adjustments have been made the output signal, which decays asa function of time, is then recorded. This is then able to bemanipulated in conventional fashion by, for example, calculating aFourier Transform and the second moment. This output signal and itsassociated temperature and/or time constitute the data of interest.

As the temperature increases, the entire procedure is repeated. Clearlythis is a very cumbersome and labour intensive procedure allowingmeasurements to be taken at about 90 second intervals (minimum)depending upon the dexterity of the operator. Where substantialadjustments are required, the time between measurements may be up to 4minutes.

The above described prior art procedures and equipment are furtherdescribed in ADVANCES IN MAGNETIC RESONANCE Volume 12 Edited by J. S.Waugh, Academic Press 1988 pages 385 to 421 ¹ HNMR Thermal Analysis byL. J. Lynch, D. S. Webster & W. A. Barton, and REVIEW OF SCIENTIFICINSTRUMENTS Volume 50 No. 3, March 1979 pages 390 & 391. D. S. Webster,L. F. Cross & L. J. Lynch.

While it is effective, this prior art measurement technique is somewhatinconvenient, especially as temperature regimes such as a temperatureramp which increases by at least 4° C. per minute with measurementsbeing taken every 30-75 seconds, are of interest.

In order to enable these faster measurements to be taken, asubstantially automatic method based upon the abovementioned BRUKERMINISPEC will now be described with reference to FIG. 2.

As seen in FIG. 2, an NMR spectrometer 100 in the form of theabovementioned BRUKER MINISPEC is provided. This prior device has a pairof permanent magnet energized pole pieces 102 which are 12.5 cm indiameter and are spaced apart by a 2.5 cm airgap. The permanent magnetsgive a magnetic field strength of the order 0.47 T. The prior art deviceis also provided with two substantially identical field windings 103located one on each of the pole pieces 102. These field windings 103enable the magnetic field strength between the pole pieces 102 to beadjusted as necessary.

The prior art device is modified as follows. Located between the polepieces 102 is a specimen probe 105 having an exterior jacket 106. Theprobe includes its own heater 107 and thermocouple 108 to respectivelyheat the specimen and measure the temperature of the specimen. Thedetails of the preferred probe 105 are as described with reference toFIGS. 3-5.

The specimen itself (not illustrated in FIG. 2) is located within an RFcoil 109 which forms part of a tuned circuit having a variable capacitor110. The jacket 106 is also provided with temperature regulation whichnormally takes the form of a water supplied temperature regulator 111known per se and schematically illustrated in FIG. 2.

In order to provide better stability of the magnetic field strength, thepole pieces 102 and associated equipment are provided with a magnetheater 104 to maintain the temperature of the magnetic circuit elevatedto a predetermined temperature approximately 10° or 20° C. above ambienttemperature. Alternatively the magnetic circuit can be located within awater bath (not illustrated) the temperature of which is controlled.

The prior art spectrometer 100 is provided with a signal receiver 113, aclock frequency source 114, a pulse programmer 115, a pulse gate/phaseselector 116, a pulse transmitter 117 and a duplexer 118 which enablespulses from the transmitter 117 to be applied to the RF coil 109 and theresultant signal received therefrom to be applied to the receiver 113.Each of the items 113-118 is substantially conventional.

Added to the prior art spectrometer is a signal digitizer or A to Dconverter 119 which has a 10 MHz sampling rate, 8 bit resolution, and2048 data points. The output of the digitizer 119 is applied to acentral processing unit (CPU) 120 which is preferably realized by meansof a personal computer. The CPU 120 is provided with various peripheralsin the form of screen 121, keyboard 122, disc drive 123, plotter 124,and printer 125.

In addition, the CPU 120 is connected to a number of controllers in theform of specimen temperature controller 131, probe tuner 132, magneticfield controller 133, and pulse width controller 136. A magnettemperature controller 134 and probe jacket temperature controller 135each with manual controls are also provided. The probe jackettemperature controller 135 ensures that the temperature of the jacket106 surrounding the sample is maintained in order to minimizetemperature gradients to which the magnetic circuit may be subjected,while the magnet temperature is itself regulated by means of themagnetic temperature controller 134.

Because the CPU 120 and spectrometer 100 are interconnected, during theheating regime (in the temperature range 25° C.-600° C. for example) inthe course of which it is intended to take measurements, the followingprocedures are carried out. Firstly, the magnetic field controller 133corrects the magnetic field strength at the sample for any small driftsin the magnetic field which may have occurred over the operating timeelapsed hitherto. This is best done by utilizing the NMR signal from thesample under test as a means of sensing the magnetic field for use infeedback control. This has the consequence that the resolution of themagnetic field setting is dependent upon the state of the sample. Thusincreased field resolution can be readily achieved with relativelyslowly decaying signals where tuning is more critical.

Secondly, the probe tuner 132 adjusts (by means of a stepping motorcontrolled mechanically variable capacitor) the resonant circuit of thesample, if necessary, in accordance with the measured temperature of thesample as measured by the specimen temperature controller 131. Again theNMR signal from the sample under test can be used in a feedback loop. Amanual temperature calibration check can also be made from time to time.

Thirdly, the pulse width controller 136 adjusts the RF power to besupplied as necessary in accordance with the measured temperature of thesample. Either a look up table based on previous experience at themeasured temperature, or the sample NMR signal incorporated in afeedback loop, can be used.

With all these pre-conditions substantially simultaneously satisfied,the transmitter 117 then transmits a series of radio frequency pulses asdetermined by the pulse programmer 115 to the RF coil 109 via duplexer118. The induced nuclear resonant signal is then transmitted to thereceiver 113, amplified and passed via the digitizer 119 to the CPU 120which records this single measurement. Specimen temperature controller131 continues to operate so as to increment the temperature of thesample (in accordance with a predetermined regime previously specifiedvia the CPU 120) and the next measurement is made. In this way a seriesof measurements can be made as the temperature of the sample increases,for example in a linear temperature ramp.

With a desired predetermined temperature regime set by the temperaturecontroller 131, a series of measurements can be taken with predeterminedintervals between measurements and/or at predetermined temperaturesthereby giving rise to a series of measurements which are stored in CPU120 or a remote memory such as a disc inserted in the disc drive 123.Alternatively, or additionally, the results can be displayed on thescreen 121, plotted on the plotter 124 and/or printed out on the printer125.

It will be apparent to those skilled in the art that the substantialadvantage offered by the spectrometer of the preferred embodiment isthat not only can the desired analysis be carried out every 30-75seconds, but also the data thereby created can be stored and analyzed.

As seen in FIG. 3, the probe 105 takes the form of an elongate body 142having a cylindrical opening 143 at its upper end and a base 144 at itslower end. The opening 143 is dimensioned to receive a sample holder 5which contains a sample to be studied. If the sample is coal, ispreferably powdered or granulated, however, the sample can equally be asolid or a liquid.

As will be explained hereafter, the thermocouple 108 is passed throughthe base 144 in order to lie below the sample holder 5 in order that thetemperature of the sample can be indirectly inferred by calibration. Theexterior of the probe 105 is covered with a thin coating ofalumina-silicate cement 147 such as AREMCO 503 manufactured by AREMCO ofthe U.S.A. The electrical connections 148 to the radio frequency (RF)coil 109 (illustrated in detail in FIG. 4) extend through the cement 147and in that region each pass through a corresponding ceramic tube 149(illustrated in FIG. 4) of short length which is embedded in the cement147. Similarly, the ends of the heating winding 107 pass through thebase 144. This arrangement prevents any inadvertent contact between theRF coil 109 and heater 107.

Turning now to FIG. 4, the interior detail of the probe 105 isillustrated. The body 142 is machined from sintered glass sold under thetrade name MACOR by Corning of the U.S.A. A double start thread 152 iscut in the exterior cylindrical surface of the body 142. A cylindricalopening 143 is drilled through the body 142. A narrow longitudinal slot154 is cut into the side of the opening 143 and extends beyond half thelength of the opening 143. A hollow cylindrical plug 151 formed fromMACOR and having a central cylindrical aperture 153 is inserted into thelower end of the opening 143. The plug 151 extends less than half thelength of the opening 143. The aperture 153 receives the thermocouple108 as indicated in FIG. 3.

Also formed from MACOR is a hollow cylindrical former 156 the internaldiameter of which is sufficient to receive the sample holder 5 and theexternal diameter of which just fits within the cylindrical opening 143.Cut into the exterior of the former 156 is a flat bottomed, wide cutthread 157 into which a silver or gold wire 158 having a rectangularcross-section (as best illustrated in FIG. 5) is wound. The free ends ofthe wire 158 constitute the electrical connections 148.

After the former 156 has been wound with the wire 158, the former ispassed into the opening 3 with the electrical connections 148 beingaligned with, and passed through, the slot 154. The former 156 is thenmoved along the cylindrical opening 143 and into its final positionillustrated in FIG. 4 which is preferably centrally located relative tothe heating winding 107. Then the heating winding 107, which is loopedback upon itself in known fashion so as to be effectively non-inductive,is wound in the double start thread 152 as illustrated in FIG. 4.Immediately after the heating winding 107 is wound into position, theentire arrangement is covered with the thin layer of cement 147 in orderto firmly locate the components in place.

It will be apparent to those skilled in the art that the abovementionedarrangement provides a number of substantial advantages. Firstly, the RFcoil 109 is held in position between the thread 157 and the interior ofthe cylindrical opening 143. Thus not only is the RF coil 109 accuratelyheld in its desired location, but it is not surrounded by any largevolume of undesirable (e.g. proton containing) material.

It will also be appreciated by those skilled in the art that thethermocouple 108 must be spaced from the sample holder 5 in order not todistort the actual measurement. In order that the thermocouple 108actually measures the temperature of the sample held in the holder 5, acalibration procedure is previously carried out. Here an additionalthermocouple is placed in a typical sample and the temperature of theprobe 105, say, increased from lowest to highest. The actual temperatureof the sample recorded by the additional thermocouple is then matchedwith the readings taken at the same time by the thermocouple 108 toarrive at a calibration adjustment for the thermocouple 108.

The foregoing describes only one embodiment of the present invention andmodifications, obvious to those skilled in the art, can be made theretowithout departing from the scope of the present invention.

For example, although the double start thread 12 illustrated in FIG. 4has its pitch distance greater than the thread to thread distance, it ispreferred that these two distances be made equal. Furthermore, althoughthe wire 158 preferably has a rectangular cross-section for use at 60MHz, for use at 20 MHz wire of circular cross-section will suffice.

Furthermore, before taking a measurement, the receiver 113 preferablyhas its gain adjusted to a known relative value so that its outputsignal amplitude is appropriate for the input voltage range of thedigitizer 119.

As the signal/noise ratio (S/N) of a single measurement is normally notlarge enough for good analysis (particularly both as the temperatureincreases and the sample loses hydrogen), this can be improved by addinga number of successive single measurements together to produce oneaveraged result. To do this the rate at which each single measurement isrepeated is set so that it is sufficiently slow to avoid NMR signalsaturation effects--otherwise the signal will be attenuated and theamplitude information may not be properly representative and analysiswould at best be difficult if not meaningless.

Alternatively, this sensitivity to measurement rate can be used in aPMRTA procedure whereby information on the NMR signal saturation, orspin lattice relaxation phenomena, can be recorded. Thus for transverserelaxation measurements the rate of measurement must be much slower thanthe spin lattice relaxation rate.

Finally, the number (NS) of successive single measurements addedtogether is preferably an adjustable parameter which is set by tradingoff the increased S/N with larger NS against the time (and hence sampletemperature change) over which these NS are acquired.

Set out in the APPENDIX hereto is the program listing of the FORTRANdata acquisition program implemented by the CPU 120. The detailedsubroutines which are referred to are not listed in detail. The steppermotor referred to is used to control an adjustable capacitor in the RFtuner 132.

COPYRIGHT NOTICE

The program listing contained in the APPENDIX is copyright and remainsthe property of COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCHORGANISATION and is not to be implemented or duplicated in written orelectronic form without the express prior written approval of thatorganisation. The publication of the program listing together with thispatent specification is with the approval of, and on behalf of, thecopyright owner. ##SPC1##

We claim:
 1. A method of carrying out proton magnetic resonance thermalanalysis measurements, said method comprising the steps of:i) locating asample within a coil forming part of an RF tuned circuit and applying amagnetic field to said sample, ii) heating said sample in accordancewith a predetermined temperature regime, iii) applying pulsed RF energyto said coil to generate a pulsed RF electromagnetic field which isapplied to said sample, and thereafter substantially simultaneously, iv)adjusting the magnitude of said magnetic field to ensure that the NMRfrequency of said sample is substantially identical to the RF frequency,v) adjusting the resonant frequency of the tuned circuit, if necessary,to compensate for temperature induced changes in the tuned circuitcomponents and sample, vi) adjusting the energy of said pulsed RF energyto obtain an optimum output from said RF tuned circuit, vii) recordingthe RF tuned circuit output as a function of either the time or thetemperature of said sample, and viii) repeating steps (iv) to (vi) asnecessary at each desired time or sample temperature to obtain anoptimum RF tuned circuit output, and repeating step (vii).
 2. A methodas claimed in claim 1 wherein the magnetic field is controlled inaccordance with the RF tuned circuit output.
 3. A method as claimed inclaim 1 wherein step (viii) is repeated a plurality of times to increasethe signal to noise ratio of the measurement, the results of theindividual measurements being added together and averaged, and thenumber of times step (viii) is repeated being adjustable.
 4. A method asclaimed in claim 3 wherein the rate at which measurements are taken inselectable in order to attain a preselected level of NMR signalsaturation.
 5. A method as claimed in claim 1 wherein steps (iv) to(vii) are repeated within a time in the range of from 30 to 75 seconds.6. A proton magnetic resonance thermal analyzer comprising an RF tunedcircuit including an RF coil into which an NMR sample is insertable,said RF coil being locatable in a magnetic field, magnetic fieldstrength means to adjust the magnitude of said magnetic field, RF pulsemeans connected to said RF tuned circuit to supply same with pulsed RFenergy, an RF controller connected to said RF pulse means to adjust themagnitude of said RF energy, an RF tuner connected to said RF tunedcircuit and a heater to substantially increase the temperature of saidsample above ambient temperature, wherein each of said magnetic fieldstrength means, said RF controller, said RF tuner and said heater isconnected to a central processing unit and is both simultaneously andindividually controlled thereby.
 7. An analyzer as claimed in claim 6wherein the output of said RF tuned circuit is connected to said centralprocessing unit via a digitising means and a storage means is connectedto said central processing unit, the output of said RF tuned circuit atthe cessation of said RF pulsed energy being stored in digital form insaid storage means.
 8. A high temperature heater probe for nuclearmagnetic resonance measurements, said probe comprising an elongate bodyhaving an opening at one end, a tubular former carrying an RF coillocated within said opening with the electrical connections to said RFcoil passing through said body, the interior of said former beingdimensioned to receive an NMR sample holder, a heater coilnon-inductively wound along said elongate body and a layer of heatresistant substantially proton deficient cement covering said heatercoil and through which said electrical connections to said RF coil pass.9. A probe as claimed in claim 8 wherein said opening in said bodycomprises a cylindrical opening having a longitudinally extending slotextending between the interior of said opening and the exterior of saidbody, said slot extending approximately half the longitudinal extent ofsaid body, and said RF coil connections passing from said openingthrough said slot to the exterior of said body.
 10. A probe as claimedin claims 8 or 9 wherein said RF coil is located in a groove cut in theexterior of said tubular former and said heater coil is located in agroove cut in the exterior of said elongate body.
 11. An analyzer asclaimed in claim 6 wherein said RF coil and heater comprise the RF coiland heater of the probe as claimed in claims 7, 8, 9 or
 10. 12. Ananalyzer as claimed in claim 6 further comprising temperature heaterprobe for nuclear magnetic resonance measurements, said probe comprisingan elongate body having an opening at one end, a tubular former carryingan RF coil located within said opening with the electrical connectionsto said RF coil passing through said body, the interior of said formerbeing dimensioned to receive an NMR sample holder, a heater coilnon-inductively wound along said elongate body and a layer of heatresistant substantially proton deficient cement covering said heatercoil and through which said electrical connections to said RF coil pass.13. An analyzer as claimed in claim 12, wherein said opening in saidbody comprises a cylindrical opening having a longitudinally extendingslot extending between the interior of said opening and the exterior ofsaid body, said slot extending approximately half the longitudinalextent of said body, and said RF coil connections passing from saidopening through said slot to the exterior of said body.
 14. An analyzeras claimed in claim 13, wherein said RF coil is located in a groove cutin the exterior of said tubular former and said heater coil is locatedin a groove cut in the exterior of said elongate body.